The outermost layer of tissue in woody plants that is resistant to the passage of water vapor and gases and that becomes the bark. Cork is secondary tissue, formed on the outside of the tissue layer known as cork cambium. The cell walls of cork cells contain suberin. Once they mature, cork cells die. Also called phellem.

The lightweight, elastic outer bark of the cork oak, which grows near the Mediterranean Sea. Cork is used for bottle stoppers, insulation, and other products.